This invention relates generally to the field of information storage, and more particularly to a circuit and method for protecting read heads of a hard-disk drive.
Hard-disk drives are mass storage devices that typically include a magnetic storage media, e.g. rotating disks or platters, a spindle motor, read/write heads, an actuator, a pre-amplifier, a read channel, a write channel, a servo circuit, and control circuitry to control the operation of hard-disk drive and to properly interface the hard-disk drive to a host system or bus. FIG. 1 shows an example of a prior art disk drive mass storage system 10. Disk drive system 10 interfaces with and exchanges data with a host 32 during read and write operations. Disk drive system 10 includes a number of rotating platters 12 mounted on a rotatable base 14. The platters 12 are used to store data that is represented as magnetic transitions on the magnetic platters, with each platter 12 coupleable to the read/write heads 18/20 which transfers data to and from a preamplifier 26. The preamp 26 is coupled to a synchronously sampled data (SSD) channel 28 comprising a read channel and a write channel, and a control circuit 30. SSD channel 28 and control circuit 30 are used to process data being read from and written to platters 12, and to control the various operations of disk drive mass storage system 10. Host 32 exchanges digital data with control circuit 30.
Data is stored and retrieved from each side of the magnetic platter 12 by the read head 18 and a write head 20. The read head comprise of magneto-resistive heads, adapted to read data from or to platters 12, when current is passed through them. Read/write heads 18/20 are coupled to preamplifier 26 that serves as an interface between read/write heads 18/20 of disk/head assembly 10 and SSD channel 28. The preamp 26 provides amplification to the waveform data signals as needed. The platter 12 surfaces are partitioned and formatted into sections as shown, with data storage wedges or sections 22 comprising the majority of the platter surface area, and smaller servo wedges 24 positioned therebetween storing positional information. At specified time intervals during the normal operation of the hard-disk drive system 10, a sequence called a Servo Bank Write (SBW) sequence is performed during which the write heads 20 write positional data to all of the platter servo wedges 24 simultaneously.
A problem with prior art hard-disk drive designs is the extreme sensitivity of the read heads 18. When data is being written to platter(s) 12 with write head 20, a large amount of current, e.g. 40 mA is placed through the write head 20, which may be coupled back into the read head 18 proximate with write head 20, possibly damaging or blowing read head 18. To prevent damage during a write sequence, most prior art designs apply a bias to read head 18. The risk of read head 18 damage is particularly high during a SBW sequence because all read heads 18 are on simultaneously and thus the bias current is divided equally between the read heads 18, resulting in the bias current applied to each read head 18 being dependent on the number of read heads 18 connected to the preamp 26. This relationship is characterized in Equation 1:             Eq.  1:        ⁢          xe2x80x83                  Ib      head        =                  I        biastotal            N      
where Ibiastotal is the total bias current applied from the preamplifier 26 to all heads 18/20, Ibhead is the bias current on one read head 18, and N is the number of heads in the hard-disk drive system 10, with N being three in the system 10 shown in FIG. 1. Thus, in transitioning to SBW mode, the bias current on a read head 18 can potentially drop from Ibiastotal in the read mode to Ibiastotal/N in SBW mode. The decreased bias current may be insufficient to protect read head 18, resulting in damage to the head 18.
What is needed is a circuit and method for protecting read heads 18 during a hard-disk drive SBW sequence.
The present invention achieves technical advantages as a circuit and method for protecting read heads of a disk drive during a SBW sequence. A feedback loop capacitor of a preamp is controllably coupled to a separate dummy head during a Vbias mode so the capacitor voltage is both predictable and lower than the voltage of the read head when returning to an Ibias mode.
The invention comprises a circuit for protecting a read head of a hard-disk drive, comprising a voltage bias circuit selectively coupleable to the read head, a capacitor selectively coupleable to the read head and a dummy head selectively coupleable to the capacitor. The dummy head may comprise an internal resistor. The capacitor is controllably and responsively coupled to the dummy head when the voltage bias circuit is coupled to the read head to prevent coupling a damaging level of current to the read head.
The invention includes a preamplifier for a hard-disk drive storage system having a plurality of platters for storing data and a read head for each the platter for retrieving the data. The preamplifier comprises a read head protection circuit having a voltage bias circuit coupleable to the read head, a capacitor coupleable to the read head and a dummy head coupleable to the capacitor. The capacitor is controllably coupled to the dummy head when the voltage bias circuit is coupled to the read head.
A method of the invention includes protecting a read head of a hard-disk drive storage system, the system comprising a preamplifier circuit having a voltage bias circuit and a capacitor coupleable to the read head, and a dummy head selectively coupleable to the capacitor. The method protects the read head by controllably discharging the capacitor voltage through the dummy head when the voltage bias circuit is coupled to the read head to prevent coupling a damaging level of current to the read head.
Advantages of the invention include protecting read heads 18 of a hard-disk drive system during a servo bank write (SBW) sequence when all of the write heads 20 are in use. The protection circuit and method are an easily implementable and dependable solution protecting read heads from being damaged during the SBW sequence. Preferably, the dummy head resistor discharges the capacitor to a predetermined voltage, rather than leaving the capacitor floating as in the prior art. The voltage is predictable and allows the storage system to remain in the Vbias mode for a longer amount of time as compared to the prior art. In some circuits, the present invention only requires an additional switch coupling the capacitor to a dummy head of the Vbias circuit.